| The stability of the power system is affected by the great fluctuation of the radar power system caused by the long pulse width operational model. Firstly, the mathematical model of the array transmitting unit was built and the concept of the current margin was put forward according to the characteristics of the average power supply mode of the pulse load. The variation rules of voltage and current of power system were analyzed by the state space segmentation method. And the system power fluctuation function and its simplified form were deduced. Secondly, the concept of PAPR (Peak-peak to Average Power Ratio) was proposed to quantitatively analyze the degree of power fluctuation. According to this index, the influ-encing factors of system of power fluctuation were analyzed, and the relationship between the power fluctuation and influencing factors was obtained. Finally, the conclusions were verified by the example analysis. They lay the theoretical foundation and have good engineering application value for power system design of radar with long pulse width operational mode.